1. Field of the Invention
The present invention relates to Blind Transport Format Detection (BTFD) for wireless communication systems.
2. Description of the Related Art
Communication systems and in particular, wireless communication system convey (i.e., transmit and/or receive) information over communication channels in accordance with protocols of one or more established communication standards. Protocols are rules and procedures that dictate how information within a communication system are to be transmitted, propagated and received. Established communication standards comprise protocols that have been reviewed and approved by committees typically formed from communication equipment manufacturers and pertinent government regulators.
In wireless communication systems, and in particular, in wireless communication system that comply with the 3 GPP (Third Generation Partnership Project) standard for UMTS (Universal Mobile Telecommunication System) systems, information that is to be transmitted are formatted in multiple modes. The information is transmitted by transmission equipment which can be either system equipment or user equipment. The system equipment are the various equipment owned, operated and maintained by a system provider. Equipment at a base station are examples of system equipment. User equipment is any equipment typically used by a user or subscriber of a wireless communication system. Examples of user equipment include cellular phones, wireless laptops and pagers.
The formatting of information refers to the arrangement of units of information (typically bits) into groups or blocks of information where the size of each block is defined. Suppose, for example, that the 3GPP standard uses eight modes to do its formatting. Each of the eight modes of the 3GPP standard arranges information to be transmitted into three blocks respectively referred to as Class A, Class B and Class C blocks. In UMTS, the Class A, Class B and Class C blocks are referred to as Transport Channels (TrCh) and each Transport Channel has a format called a Transport Format (TF). The modes typically are the operating modes of Codecs which are devices and/or functions within the system equipment and/or subscriber equipment that perform the coding operations. The following is a table showing the format for each of the eight modes for UMTS systems that comply with the 3GPP standard:
TABLE 1ModeClass AClass BClass Cmode 181 bits103 bits 60 bits mode 265 bits99 bits40 bits mode 375 bits84 bits0 bitsmode 461 bits87 bits0 bitsmode 558 bits76 bits0 bitsmode 655 bits63 bits0 bitsmode 749 bits54 bits0 bitsmode 839 bits56 bits0 bits
After the information to be transmitted is arranged, i.e., formatted, as per one of the above modes, each of the groups of information is coded for error correction and/or error detection. Coding is a technique whereby redundancies are introduced in information to be transmitted to protect the information from having errors due to the information having been propagated through a communication channel. Error correction coding is used to correct errors and error detection coding is used to detect errors. The formatted information is subjected to various levels of coding and information padding. In particular, for UMTS systems, the formatted information is applied to a Cyclic Redundancy Coder (CRC) and tail bits are then added to pad the coded information. The formatted, coded and padded information is then applied to a convolutional coder. The output of the convolutional coder is the information coded through special mapping of every unit of the information. For example, for a convolution coder which maps 2 bits for every 1 bit of information (i.e., Rate ½ coding), the total number of bits for each transport channel is doubled. Convolutional coded information for each of the three transport channels is thus generated. Convolutional coding is one type of error correction coding. CRC coding is one type of error detection coding. The information of the three channels are then multiplexed prior to transmission.
FIG. 1 depicts an example of a format of the transport channels of a UMTS that complies with the 3GPP standard. Information block 100 represents the format for a transport channel which contains A bits of information with an appendage of 8 CRC bits and 8 tail bits; this transport channel is commonly referred to as TrCh1. Information block 102 represents the format for a transport channel which contains B bits of information with 8 tail bits appended; this transport channel is commonly referred to as TrCh2. Information block 104 represents the format for a transport channel which contains C bits of information and 8 tail bits; this transport channel is commonly referred to as TrCh3.
The multiplexed information is then transmitted over a communication channel or channels of the UMTS system. In UMTS systems the information is transmitted in synchronization with a timing period called a TTI (Transmission Time Interval). Transmitting equipment and receiving equipment of the system are synchronized to the TTI. Each TTI period has a beginning and an end; three blocks as per Table 1 are transmitted during a TTI. At a receiving equipment, a Class A block is first received followed by a Class B block and then a Class C block. The size of each of these received blocks is dictated by the mode in which the system is currently operating.
At a receiving equipment, the information is decoded by applying procedures that are the reverse of the procedures applied by the transmitting equipment. As with the transmitting equipment, the receiving equipment can be system or subscriber equipment. In order to properly decode the formatted information, however, the receiving equipment uses the actual coded block of information and information about the formatting (i.e., size of the blocks of information over each of the transport channels) of the received block. In particular, a received coded and formatted block of information is decoded by using the actual block and the size of that block to decode (e.g., CRC decoding, convolutional decoding) the received information. For example, referring to Table 1, a Class A block of information is properly decoded when that block of information is applied to a decoder of the receiving equipment and the decoding uses the correct size value (i.e., the value of 81) to perform the decoding operation. If the size value used by the decoder is incorrect, the received block will not be decoded correctly.
To address the issue of knowing the correct block size, the current UMTS standard uses a signaling channel within which TFCI (Transport Format Combination Indicator) information is transmitted to the receiving equipment. The TFCI contains the value that represents the size of the received block. In the example discussed above, the TFCI would contain the value of 81 for a Class A block, 103 for a Class B block and 60 for a Class C block. Because the decoding of the received information is dependent upon a correct size value for a received block of information, the TFCI is typically heavily coded and made more robust so as to better handle channel anomalies thus reducing the likelihood of incurring errors. As a result, more bandwidth and power is needed to transmit the TFCI. Furthermore, even though the heavy coding of the TFCI reduces the likelihood of errors occurring in the TFCI, an error bound still exists. The error bound is the best error rate that can be expected from TFCI for the type and amount of coding applied to the TFCI.
What is therefore needed is a way of detecting the format of received information without having to use TFCI.